1. Field of the Invention
The present invention relates to a Platinum Group Metal (PGM) catalyzed addition-curable organopolysiloxane compositions having an extended shelf and work life. More particularly, the present invention is directed to the employment of a PGM catalyst inhibitor in a heat curable organopolysiloxane composition, where the PGM catalyst inhibitor is a halogenated organic compound having at least one olefinic or acetylenic group.
2. Discussion of the Prior Art
As shown by C. A. Sumpter et al, U.S. Pat. No. 5,331,075, addition curable organopolysiloxane compositions are well known in the art. A typical addition curable organopolysiloxane composition involves an addition reaction in the presence of an effective amount of a PGM catalyst, such as a platinum or rhodium catalyst, between a "vinylpolysiloxane" and a multi-hydrogen functional silicon-hydride material, such as a "silicon hydride siloxane". The vinylpolysiloxane can be an organopolysiloxane having alkenyl radicals, for example, vinyl radicals attached to silicon by carbon-silicon bonds. Usually, the PGM catalyst is employed as a mixture with the vinyl polysiloxane prior to contact with the multi-hydrogen functional silicon-hydride material. Upon mixing the various ingredients, crosslinking or cure, often occurs within seconds at ambient temperatures.
In order to increase work time, the "two part mixture" approach is sometimes used. The first part, or "part one" can be a mixture of an effective amount of the PGM catalyst, and the vinyl organopolysiloxane; "part two" can be a mixture of the silicon hydride siloxane and the balance of the vinyl organopolysiloxane.
While the two part mixture is often used, the preferred procedure is to provide a "one part mixture" of all of the ingredients. Even though all the ingredients are mixed together, the one part mixture can have an extended shelf life at ambient temperatures. In addition, the one part mixture preferably can exhibit a rapid cure, such as within 10-30 minutes, when heated at temperatures in the range of about 120.degree. C. to about 150.degree. C.
Various procedures have been developed in the art to achieve effective results with one part mixtures. While two part mixtures have the advantage of an indefinite shelf-life over a wide temperature range, in order to achieve the desired advantages in the one part mixture, the PGM catalyst must be rendered inactive, or "masked" at ambient temperatures. However, the PGM catalyst can be reactivated at the command of the end user at an appropriate higher temperature.
Several procedures have been developed for masking the activity of the PGM catalyst at ambient temperatures. For example, a latent platinum catalyst is shown as a preform with an organic-nitrogen compound in U.S. Pat. No. 5,331,075; an encapsulated form of platinum catalyst, is taught in U.S. Pat. No. 5,015,691. In addition, certain unsaturated materials, such as a maleate, or acetylenic alcohol have been found to function as inhibitors when added directly to a PGM catalyzed hydrosilylation mixture. However, the weight level required to achieve effective inhibition results with such added unsaturated materials can lead to environmental release problems, based on the excessive quantities required. It would be desirible therefor to identify effective PGM inhibitors which could be added directly to to PGM catalyzed hydrosilylation mixtures to provide useful one part heat curable mixtures.